Would Sony be happy with 5% for letting Disney use their most profitable character? Or would they feel like Spider-Man would increase the box office take of Avengers more than 5% and they'd be getting gipped?

It would make enough cash to spread around, and you'd think that the terms would be pretty simple, but honestly, why would Sony not be down for letting Spidey being in Avengers 2? Not forcing it, because I like Spidey as the hero fighting on the streets day to day than him as part of a team, but it makes sense to me for them to actually do so. They're not spending money.